Nourizadeh, a commentator for Deutsche Welle and the Voice of America with an extensive network of contacts in Iran, said the explosion caused relatively little damage to the uranium enrichment facility itself. But the blast has blocked the entrance to Fordow, he confirmed, and more than 200 personnel are trapped in the plan.

A report published on Right-wing news website WND on Friday, quoting a defected Iranian intelligence officer, claimed that a massive blast had ripped through the nuclear facility, buried deep within the guts of a large mountain.

The alleged blast was said to have erupted at 11.30am last Monday – on the eve of the Israeli election – partially destroyed the nuclear site and trapped 240 people underground. Tehran held Israel responsible, the report said.